Alkaline phosphatase is known to be subject to a very complex control which has been investigated for over a decade but much has still to be resolved. A new approach for the genetic analysis of alkaline phosphatase (phoA) gene expression in Escherichia coli is proposed. A through understanding of phoA gene expression is extremely important both because phosphate metabolism plays a central role within all cells and because alkaline phosphatase (the product of the phoA gene) is a bacterial example of a secreted protein. Thus, this study bears direct relevance to problems of gene expression in higher systems, such as immunoglobin synthesis. Largely, this study is based upon the application to the phoA system of the in vivo gene fusion technique developed by Casadaban (J. Mol. Biol. 104: 541-555 1976). This novel approach to the study of PhoA expression should help elucidate the molecular basis of phoA gene expression. Specifically, this study is aimed towards four goals: (1) the isolation of promoter and operator mutations of the phoA gene; (2) a deletion analysis of the phoA gene; (3) a genetic analysis of the phoB-phoR region (which is involved in phoA regulation); and (4) the isolation and characterization of new regulatory mutants affecting different steps in phoA expression.